Optical access networks, such as point to multipoint optical access networks are known in the art. ITU-T Recommendation G.983.1 defines an access network that utilizes optical fiber technology to convey point to multipoint downstream traffic from an headend such as an Optical Line Termination (OLT) to multiple network units such as Optical Network Units (ONUs) or Optical Network Terminations (ONTs) and to convey point to point upstream traffic from an ONU or ONT to the OLT.
An ONU provides, either directly or remotely, the user-side interface of the Optical Access Network (OAN).
An OLT provides the network side interface of the OAN and is connected to at least one Optical Distribution Network (ODN).
An ODN provides the optical transmission means between the OLT and the ONUs. An ODN usually includes passive optical components such as optical fibers, optical connectors, passive branching components, passive optical attenuators and splices.
The optical access network supports Asynchronous Transfer Mode (ATM) based data transmission. ATM based data transmission allows to support more than a single class of service. When a packet, such as but not limited to Internet Protocol (IP) packet, is received at an ATM supporting network, it is segmented to provide a group of at least one ATM cell. Each ATM cell is routed across the ATM based network. Before exiting the ATM based network the IP packet is reassembled from the at least one ATM cell.
Each ATM cell is 53 bytes long and includes a 7-byte header and 48-byte payload. The ATM header is utilized for routing ATM cells across the ATM based network.
As multiple network units, such as ONUs or ONTs share the same media, the OLT controls upstream transmission, by assigning upstream timeslots by implementing a Media Access Control (MAC) scheme. According to the ITU-T Recommendation G.983.4 upstream bandwidth may assigned in two manners—(a) in response to the utilization of upstream bandwidth by each of the ONUs, and (b) in response to upstream status reports from the ONUs or ONTs. More specifically, each ONU (or ONT) can include at least one Transmission Container (T-CONT), each T-CONT has at least one queue. An ONU reports the queue length of T-CONTs that belong to him. Usually, a single T-CONT has more than a single queue, each queue associated with a distinct class of service. Accordingly, the aggregate queues length of that TCONT is reported.
An ONU (or ONT) can selectively report the T-CONTs queue length by various manners. For example, An ONU (or ONT) can report the queues lengths from the most congested T-CONT, from each T-CONT in turn equally, but this is not necessarily so. These reports are transmitted upstream in mini-slots assigned by the OLT.
Upstream traffic is arranged in an upstream frame of 53 timeslots. Each timeslot consists of three-bytes of PON layer overhead and either an ATM cell or a PLOAM cell.
The OLT allocates upstream bandwidth on a timeslot to timeslot basis, according to the T-CONTs queue length and then transmits downstream data grants in downstream PLOAM cells. Assuming that the upstream and downstream bit rate are the same, then during a frame of 53 timeslots, two PLOAM cells are utilized for providing 53 data grants, corresponding to the 53 timeslots within each upstream frame. When the upstream data rate is much smaller than the downstream data rate, some PLOAM cells are empty.
The T-CONTs are classified to five types, each type is characterized by an assigned bandwidth out of the following five assigned bandwidth types: (i) fixed bandwidth, (ii) assured bandwidth, (iii) non-assured bandwidth, (iv) best effort bandwidth, and (v) maximum bandwidth. It is noted that the first four assigned bandwidths are listed according to their priority, starting with the highest priority assigned bandwidth. Accordingly, the assignment of bandwidth starts by assigning bandwidth to fixed bandwidth. The assignment limits the amount of cell transfer delay and delay variation. Assured bandwidth is assigned using the remaining bandwidth. Assured bandwidth means that a predefined average (long-range) bandwidth is assigned. It is noted that the amount of allocated bandwidth per frame can fluctuate. The yet remaining bandwidth (also referred to as surplus bandwidth) is utilized for the lower priority bandwidth assignments such as the non-assured bandwidth and the best effort bandwidth.
A type 1 T-CONT is characterized by fixed bandwidth only. Bandwidth is allocated to a type 1 T-CONT regardless of whether its queues are empty or not. A type 2 T-CONT is characterized by assured bandwidth only.
A type 3 T-CONT is characterized by assured bandwidth and non-assured bandwidth. A type 3 T-CONT shall be allocated bandwidth equivalent to its Assured bandwidth, only when it has cells at a rate equivalent to Assured bandwidth or more than Assured bandwidth. Non-assured bandwidth shall be allocated across T-CONTs with Assured bandwidth, and by requesting surplus bandwidth in proportion to the Assured bandwidth of the individual T-CONT on the PON, e.g., Weighted Round Robin method, as surplus bandwidth. The sum of the assured bandwidth and non-assured bandwidth allocated to this T-CONT should not exceed its maximum bandwidth, which is pre-provisioned.
A type 4 T-CONT is characterized by best effort bandwidth only and does not have any guaranteed bandwidth. A type 4 T-CONT shall only use bandwidth that has not been allocated as fixed bandwidth, assured bandwidth and non-assured bandwidth to other T-CONTs sharing the same upstream bandwidth. Best-effort bandwidth is allocated to each type 4 T-CONT equivalently, e.g., based on Round Robin method, up to their predefined maximum bandwidth.
A type 5 T-CONT is the super set of type 1-type 4 T-CONTs. Accordingly they can be characterized by at least one of the following assigned bandwidths: fixed bandwidth, assured bandwidth, non-assured bandwidth and best-effort bandwidth. It is noted that the bandwidth allocation cannot exceed the maximum bandwidth of the T-CONT.
It is noted that a T-CONT may have a priority control mechanism and/or an internal schedule that are operable to determine from which class of service queue to transmit an ATM cell in response to a data grant.
It is further noted that each assigned bandwidth type may be associated with its own class of service. Accordingly, the five mentioned above type of bandwidth assignment are associated with five class of service.
U.S. Pat. No. 5,926,478 of Ghaibeh et al. titled “Data transmission over a point-to-multipoint optical network” describes a data transmission protocol for use in an ATM based point-to-multipoint passive optical network interconnecting a headend facility and a plurality of network units. The headend facility controls the upstream transmission from the network units in response to ATM cell queue sizes at the network units and in response to a selected set of service priorities. A network unit can include various queues, such as a CBR queue, a VBR queue and a ABR queue. The sizes of these queues are included within an upstream bandwidth request.
Downstream data is transmitted in serial data frames comprising one hundred eighty, fifty-four byte downstream slots, including two framing slots and one hundred seventy-eight ATM cell slots. Each downstream frame slot includes a one byte MAC overhead header field for transmitting upstream transmission permits allocated over twenty bit permit fields, for a total of seventy-two upstream permits allocated per downstream frame. The downstream frames are transmitted every 125.mu.sec for an overall downstream bit rate of 622.08 Mbps. Upstream data is transmitted from an individual network units in five hundred forty bit upstream data slots, each upstream slot having a preamble portion and a payload portion, i.e., with seventy-two upstream slots are transmitted every 125.mu.sec, thereby forming upstream frames received at the headend at a data rate of 311.04 Mbps.
End users negotiate with service providers to determine a class of service or service level. A service Level Agreement (SLA) defines traffic parameters from the end-user, throughout at least one network that interconnect the end-user with other end-users or with other service providers. The traffic parameters include overall delay, delay fluctuations, bandwidth allocation and the like. Many users generate and receive variable length packets, such as Internet Protocol (IP) packets. In such cases the SLA relates to the transmission of IP packets, and does not necessarily comply with the transmission and routing of ATM cells originating from the IP packets.
The size of the IP packet is smaller then the aggregate size of ATM cells the originate from the IP packet, as a header of 7 bytes is added to each 48 bytes of IP packet. Assuming that the size of the IP network is S1=A*48+B, then the aggregate size of the ATM cells that originate from the IP packet (S2) equals: S2=53*(trunc (S1/48 byte)+1)=53*(A+1). It is noted that the (A+1)'th ATM cell includes B bytes originating from the IP packet and (48−B) “stuffing” bytes. The utilization of the ATM network equals S2/S1. S1 is also referred to as the length of the relevant payload and (S2−S1) is also referred to as the overhead signals. ATM network arbitration and scheduling schemes are based upon the overall aggregate size of ATM cells (including header and stuffing bit) that are stored within queues, and not according to the aggregate “net” payload of the cells and neither upon the length of each group.
Furthermore, ATM policing schemes, such as RED or WRED schemes that determine when to discard incoming traffic in response to various parameter such as traffic load are also cell oriented. Accordingly, most of the ATM cells originating from the same IP packet can be routed across an AT1VI network just to see that one ATM cell was discarded, thus all the ATM cells must be re-routed across the network.
As ATM cells are routed on a cell to cell basis, in the presence of ATM cells from many sources, consecutive cells originating from the same IP packet are not routed in a consecutive manner, thus increasing the overall delay and the delay jitter across the ATM network, and require extensive allocation of memory resources.
There is a need for a system and method for improved bandwidth utilization.
There is a need for a system and method for a media access control method and controller that are based upon relevant payload.
There is a need for a system and method and for allowing the routing of ATM cell groups.